1. Technical Field of the Invention
The present invention relates to a method for producing a surface-treated steel sheet, a surface treated steel sheet, and an organic resin coated metal container.
2. Description of the Related Art
For steel sheets used in fields of home electronic appliances, building materials, vehicles, aircrafts, and containers, etc., chromate treatment is known as the treatment to improve adhesiveness to organic resin to be formed on the surface and for its excellent corrosion resistance and adhesiveness the treatment has been widely used.
For example, for tin-plated steel materials and tin-based alloy-plated steel materials used for metal containers such as cans for food and beverage, a chromate treatment where cathode electrolytic treatment is performed in an aqueous solution of dichromate sodium is used. Surfaces of the tin-plated steel materials and tin-based alloy-plated steel materials for which such chromate treatment is performed exhibit excellent adhesiveness to organic resin that an organic resin barrier layer can be successfully formed by coating or laminating, etc.
However, hexavalent chromium used in the chromate treatment is toxic and there is a problem that it imposes a large environmental burden. Further, in the chromate treatment, although the treatment can be performed in a way that does not leave hexavalent chromium in the final products to be produced and cause harm to users, in recent years, because there is a growing trend to reduce and eliminate use of any compounds containing chromium including hexavalent chromium, etc., and also because a large amount of expenses are required for wastewater treatment, exhaust gas treatment, waste disposal, etc., resulting from the chromate treatment, there is a demand to develop a non-chromium surface treatment to replace the chromate treatment.
As for the non-chromium surface treatment to replace the chromate treatment, there has been proposed, for example, treatment in which a steel sheet is immersed into a treatment liquid containing Zr (zirconium) or Ti (titanium) (Patent Document 1: International Publication No. WO 2002/103080). However, as to a surface-treated steel sheet obtained by immersion to such treatment liquid containing Zr or Ti, corrosion resistance is insufficient in a formed coating. Also, because its coating deposition speed is slow compared to an electrolytic chromic acid treated steel sheet (TFS) which has been conventionally used as a material for cans, there is a problem of significant deterioration in productivity. For these reasons, as a high-speed treatment process to take over the treatment by immersing the steel sheet into a treatment liquid, there has been proposed a cathode electrolytic treatment using an electrolytic treatment solution containing Zr or Ti, which is known for generating a metal-oxygen compound to the steel sheet surface at a high-speed (Patent Documents 2: Japanese Patent Application Publication No. 2004-190121 A and Patent Documents 3: Japanese Patent Application Publication No. 2005-97712 A).
More, as for the non-chromium surface treatment to replace the chromate treatment, there has been also proposed a surface-treated steel sheet where a coating of aluminum oxide with corrosion resistivity is formed to the surface of the steel sheet by cathode electrolytic treatment using an electrolytic treatment solution containing Al (aluminum) (Patent Document 4: Japanese Patent Application Publication No. 2006-348360 A).